Refractory for milling

Abstract

To suppress cracking due to thermal shock at the initial stage of operation in a refractory material for iron making containing silicon carbide and titania.SOLUTION: A refractory for iron making according to the present invention contains in a refractory composition of 100 mass%: 5 mass% or more and 35 mass% or less of silicon carbide fine powder having a particle diameter of less than 0.3 mm; 3 mass% or more and 20 mass% or less of titania fine powder having a particle diameter of less than 0.3 mm; and 6 mass% or less of metallic silicon fine powder having the particle diameter of less than 75 μm, and it has a carbon black content of 5 mass% or less (including 0), wherein the content (Si) of the metallic silicon fine powder, the content (TiO2) of the titania fine powder, and the content (C) of the carbon black satisfy the following formula (1). Si / TiO2≥0.11*C+0.1...formula (1).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to refractories for steelmaking, such as pouring materials, pressure-fed materials, precast blocks, spraying materials, trowel coating materials, or ramming materials, which are used in blast furnaces, blast furnace troughs, hot metal ladles, hot metal furnaces, etc.

Background Art

[0002] In refractories for steelmaking, technologies that ensure corrosion resistance by using a large amount of silicon carbide and carbonaceous raw materials are widely used. However, with the oxidation of silicon carbide and the like, a decrease in corrosion resistance may become a problem. As a countermeasure, for example, it has been proposed to use titanium carbide as a raw material for refractories as described in Patent Document 1. However, since titanium carbide is expensive, using titanium carbide as a raw material for refractories is not industrially practical.

[0003] On the other hand, for example, Patent Document 2 proposes a technology that aims to maintain and improve corrosion resistance by reacting titania and silicon carbide during operation to form titanium carbide. That is, Patent Document 2 discloses an amorphous refractory characterized in that, in 100% by mass of the refractory composition, it contains 5 to 35% by mass of silicon carbide fine powder having a particle size of 0.3 mm or less and 3 to 20% by mass of titania fine powder having a particle size of 0.3 mm or less as refractory fine powder, and contains 0.5 to 8% by mass of alumina cement as a hardening agent. And Patent Document 2 describes that titanium carbide and titanium carbonitride are generated by the reaction of silicon carbide and titania, and it is shown in the examples that it has excellent corrosion resistance in an induction furnace erosion test using hot metal and blast furnace slag as erosive agents.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When the present inventors conducted an evaluation of cracks in the unshaped refractories of Patent Document 2 assuming actual machine use in the laboratory, it was found that cracks occurred significantly. And it was found that this cracking phenomenon occurs significantly, for example, in a blast furnace trough when, after the casting material is constructed, the constructed body that has undergone drying is directly exposed to high-temperature slag and hot metal at the initial stage of operation.

[0006] Therefore, the problem to be solved by the present invention is to suppress cracks due to thermal shock at the initial stage of operation in a refractory for steelmaking containing silicon carbide and titania.

Means for Solving the Problems

[0007] The present inventors have found that in a refractory for steelmaking containing silicon carbide fine powder and titania fine powder, the thermal shock resistance is significantly improved by containing metallic silicon fine powder in a specific mass ratio with respect to the titania fine powder. This will be specifically described below.

[0008] In a refractory containing silicon carbide fine powder and titania fine powder, titanium carbide and carbonitride fine particles are generated in a high-temperature range (the temperature of the refractory in the steelmaking process is about 1350 °C or higher and 1600 °C or lower), and these fine particles aggregate with each other. Along with this aggregation, shrinkage occurs inside the refractory. And along with this shrinkage, the internal structure of the refractory is damaged, leading to cracking and spalling of the entire refractory. This cracking phenomenon hardly occurs when the heating rate or heat reception rate is small, but it has been found that it almost certainly occurs when there is a large temperature change such as a sudden receipt of hot metal from a temperature of several hundred degrees.

[0009] Here, when the metal silicon fine powder is contained in a specific mass ratio with respect to the titania fine powder, the metal silicon fine powder is oxidized to generate silica in the fine powder region, and a new solid is generated between particles larger than the fine powder region. As a result, a state is formed as if there were struts inside the refractory, and the tissue structure is stabilized. In such a stabilized tissue structure, even when exposed to a rapid heating condition where the time from normal temperature to high temperature is short and the temperature gradient generated inside the refractory is large, the generation of titanium carbides and carbonitride fine particles in the high temperature region and the shrinkage of the fine powder region accompanying their aggregation are restricted, and it has been found that the occurrence of cracks and the like can be suppressed.

[0010] Furthermore, in order to prevent over-sintering and suppress slag infiltration in the trough material and the like, carbon black, which is a carbon fine powder with an average particle size of 1 μm or less, may be added. However, it has also been found that when silicon carbide fine powder coexists with titania fine powder and carbon black, cracks will occur unless more metal silicon fine powder is added compared to the case where they do not coexist.

[0011] The present invention was conceived based on the above findings, and the gist thereof is as follows. A refractory for milling, containing 5% by mass or more and 35% by mass or less of silicon carbide fine powder with a particle size of less than 0.3 mm, 3% by mass or more and 20% by mass or less of titania fine powder with a particle size of less than 0.3 mm, and 6% by mass or less of metal silicon fine powder with a particle size of less than 75 μm in 100% by mass of the refractory composition, and the carbon black content is 5% by mass or less (including 0), and further, the content of metal silicon fine powder (Si), the content of titania fine powder (TiO2), and the content of carbon black (C) satisfy the following formula (1). Si / TiO2≧0.11×C + 0.1 … Formula (1)

Effect of the Invention

[0012] According to the present invention, in a refractory for milling containing silicon carbide and titania, cracks due to thermal shock in the initial stage of operation can be suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Mode for Carrying Out the Invention

[0014] As described above, in the formula (1) of the present invention, "Si" is the content of metallic silicon fine powder which is metallic silicon with a particle size of less than 75 μm, "TiO2" is the content of titania fine powder which is titania with a particle size of less than 0.3 mm, and "C" represents the content of carbon black. Also, these "contents" refer to the mass ratio in 100% by mass of the refractory composition. That is, in the formula (1), "Si / TiO2" means the mass ratio of metallic silicon fine powder to titania fine powder. Therefore, in the following description, "Si / TiO2" is referred to as the "Si / TiO2 ratio".

[0015] When the refractory composition for steelmaking of the present invention does not contain carbon black, the above formula (1) becomes Si / TiO2 ≥ 0.1. That is, it is a requirement that the Si / TiO2 ratio is 0.1 or more. That is, when the Si / TiO2 ratio is less than 0.1, the thermal shock resistance becomes insufficient. On the other hand, when the content of metallic silicon fine powder exceeds 6% by mass, excessive silica is generated as a by-product, leading to a decrease in corrosion resistance. That is, since silica has a high dissolution rate in slag, the erosion rate of a refractory containing excessive silica increases. Therefore, in the present invention, the upper limit of the content of metallic silicon fine powder is set to 6% by mass.

[0016] On the other hand, when the refractory composition for steelmaking of the present invention contains carbon black, when the carbon black in the refractory reacts with titania fine powder to generate titanium carbide due to heating during use, the solid volume decreases and shrinks before and after the reaction. Therefore, it is necessary to increase the amount of metallic silicon according to the content of carbon black to cancel out the decrease in solid volume. Therefore, when various tests were conducted, it was found that it is necessary to satisfy the formula (1).

[0017] Figure 1 shows the results of plotting the thermal shock test of refractory materials for steelmaking assuming the pouring material for blast furnace troughs under conditions where the carbon black content and Si / TiO₂ ratio in the refractory composition are different. In Figure 1, ○ indicates those without cracks or fractures, and × indicates those with cracks and fractures. The solid line in Figure 1 is an approximate straight line based on three points: (carbon black content, Si / TiO₂ ratio) = (0, 0.1), (2, 0.35), and (5, 0.65). Specifically, with the intercept being (0, 0.1), it is linearly approximated by the least squares method, and the equation representing this straight line is the above equation (1). Note that the results of this thermal shock test are those obtained under the same conditions as the examples based on the material of Example 14 described later.

[0018] In the refractory material for steelmaking of the present invention, the refractory composition contains silicon carbide fine powder with a particle size of less than 0.3 mm in addition to the above-mentioned titania fine powder and metallic silicon fine powder. That is, in the present invention, in order to ensure corrosion resistance, particularly slag resistance, silicon carbide fine powder is used as a carbon source for generating titanium carbide from titania fine powder at a content rate of 5% by mass or more and 35% by mass or less. When the content rate of silicon carbide fine powder is less than 5% by mass, slag resistance is insufficient and the amount of titanium carbide generated is insufficient, resulting in insufficient slag resistance from this aspect as well. On the other hand, when the content rate of silicon carbide fine powder exceeds 35% by mass, the corrosion resistance to hot metal decreases. As the silicon carbide fine powder, any that is generally used as a raw material for refractories can be used without problems. Also, those with a purity of silicon carbide of 85% by mass or more can be used.

[0019] Also, the titania fine powder is used at a content rate of 3% by mass or more and 20% by mass or less in order to improve corrosion resistance by becoming a carbide during use. When the content rate of titania fine powder is less than 3% by mass, the generation of carbide is small, resulting in insufficient corrosion resistance. On the other hand, when the content rate of titania fine powder exceeds 20% by mass, there are too many fine powder parts, making it difficult to ensure the uniformity of the structure. For example, in the case of a pouring material, the fluidity is likely to be impaired. As the titania fine powder, any fine powder that is generally used as a raw material for refractories can be used without problems. Also, titania with a purity of 90% by mass or more can be used. Furthermore, from the viewpoint of improving corrosion resistance, the purity can be 93% by mass or more. Note that the particle size of the titania fine powder is less than 0.3 mm, but finer particle sizes, for example, less than 44 μm in particle diameter, and further those with an average particle diameter of 1 μm or less can also be used.

[0020] Also, as the titania fine powder, by using one that has been subjected to an easy-dispersibility surface treatment (hereinafter referred to as "easy-dispersibility surface treatment type"), in particular, the adsorptivity of a dispersant widely used in a castable material increases, and a castable material with good fluidity can be obtained. The easy-dispersibility surface treatment of titania is to coprecipitate sodium aluminate, aluminum sulfate, sodium silicate, etc. with sulfuric acid or sodium hydroxide and perform an inorganic treatment on the surface of titania by a wet method, which modifies the interfacial potential of titania. By using the easy-dispersibility surface treatment type of titania fine powder in this way, in particular, in the case of a castable material, it becomes easier to ensure fluidity at low moisture. Also, when performing molding such as pressing, it can be made into low moisture / low liquid phase, and a dense structure can be easily obtained.

[0021] In the refractory for steelmaking of the present invention, in the refractory composition, as other refractory raw materials, fused products or sintered products such as alumina, spinel, mullite, magnesia, zirconia, etc., and silica fume, clay, zircon, silicon nitride, carbon materials, etc. can be used as necessary. Also, as the carbon materials, graphite powder, pitches, etc. can be used.

[0022] The refractory for steelmaking of the present invention is a refractory used in a steelmaking process that uses water as kneading water and is manufactured by heat treatment at 1200°C or lower after molding. More specifically, it can be made into monolithic refractories such as a castable material, a precast block, a sprayed material, a trowel coating material, and a ramming material. Among these, the castable material for a blast furnace trough contains a large amount of silicon carbide and requires corrosion resistance, so by applying the present invention, those excellent in corrosion resistance and thermal shock resistance can be obtained, making it optimal as the use of the present invention.

[0023] When using the refractory for milling of the present invention as a casting material, a binder generally used in conventional casting materials can be used. For example, water-soluble binders such as alumina cement, silica sol, alumina sol, sodium silicate, sodium aluminate, and phosphates can be used. The content of the binder in the refractory composition can be 0.5% by mass or more and 5% by mass or less based on the solid content ratio. Furthermore, a dispersant generally used in conventional casting materials can also be used. Examples of the dispersant include sodium tripolyphosphate, sodium hexametaphosphate, sodium ultrapolyphosphate, acidic sodium hexametaphosphate, sodium polymetaphosphate, polyacrylate, polycarboxylate, β-naphthalenesulfonate, naphthalenesulfonic acid, melamine sulfonate, and the like. The content of the dispersant in the refractory composition can be 0.01% by mass or more and 1% by mass or less. Moreover, a drying accelerator and an antioxidant generally used in conventional casting materials can also be used. As the drying accelerator, organic fibers, foaming agents, basic aluminum lactate, etc. can be used. Specific examples of the organic fibers are polymer organic fibers such as vinylon (including polyvinyl alcohol), rayon, polyester, nylon, polypropylene, and polyethylene. As the antioxidant, borides, glass powder, etc. can be used. In addition, similarly, in the case other than the casting material, binders and dispersants used in conventional spraying materials, trowel coating materials, ramming materials, etc. can be used.

[0024] Here, the particle size referred to in the present invention is the size of the sieve mesh when the refractory raw material particles are sieved and separated. For example, metallic silicon with a particle size of less than 75 μm means metallic silicon that passes through a sieve with a mesh size of 75 μm, and metallic silicon with a particle size of 75 μm or more means metallic silicon that does not pass through a sieve with a mesh size of 75 μm. Also, the average particle size referred to in the present invention means the volume average particle size corresponding to the central cumulative value (D50) of the cumulative curve measured by a laser diffraction scattering type particle size distribution analyzer.

Examples

[0025] Table 1 shows the refractory compositions in the examples and comparative examples of the present invention and the evaluation results of the obtained refractories. In the refractory compositions of each example shown in Table 1, as the spinel, an electrically fused spinel with 72% by mass of Al2O3 and 28% by mass of MgO and a particle size of less than 8 mm was used. As the titania fine powder, one with 93% by mass of TiO2 and an average particle size of 1 μm or less was used. As the silicon carbide fine powder, one with 95% by mass of SiC and a particle size of less than 75 μm was used. As the carbon black, one with 98% by mass of C and an average particle size of 1 μm or less was used. As the calcined alumina, one with 99% by mass of Al2O3 and an average particle size of 4 μm or less was used. Also, except for Example 17, a readily dispersible surface-treated type of titania that was subjected to a readily dispersible surface treatment using a combination of alumina and silica hydrates was used. In Example 17, a non-readily dispersible surface-treated type that was not subjected to a readily dispersible surface treatment was used.

[0026] [Table 1]

[0027] Using the kneaded material obtained by adding water at an addition rate of 5% by mass to 100% by mass of the refractory composition of each example and kneading, the evaluation of thermal shock resistance, corrosion resistance, and fluidity was carried out in the following manner. <Thermal Shock Resistance> The above kneaded material was vibrated and poured into a mold of 40 × 40 × 160 mm, and specimens were obtained through curing (at 20°C for 24 hours) and drying (at 110°C for 24 hours). Next, the specimens were heated at 500°C for 3 hours. The reason for heating at 500°C is that when immersed in hot metal at 1550°C, there is a risk of explosion if volatile components such as moisture derived from the binder remain. The crucible was set in a high-frequency induction furnace. After confirming that the pig iron had melted in the furnace and reached 1550 °C, the test piece was put into the molten iron. After 20 minutes, the test piece was pulled out, and the thermal shock resistance was evaluated by visually checking whether cracks or fractures had occurred. Specifically, when no cracks or fractures occurred after pulling out, it was rated as ◎ (qualified (excellent)); when microcracks occurred, it was rated as 〇 (qualified (good)); when cracks and fractures of medium or higher degree occurred, it was rated as × (unqualified). <Corrosion resistance> The above kneaded mixture was vibrated and poured into a mold, and after curing (at 20 °C for 24 hours) and drying (at 110 °C for 24 hours), test pieces were obtained. Then, the test pieces were set on the furnace wall of the high-frequency induction furnace. After confirming that the pig iron had melted in the furnace, blast furnace slag was put on it for corrosion resistance evaluation. The test temperature and time were 1550 °C × 6 hours. The dimensional difference of each test piece before and after the test was taken as the corrosion loss dimension, and the corrosion loss index was obtained with the corrosion loss dimension of Comparative Example 1 set as 100. The smaller the value of this corrosion loss index, the better the corrosion resistance. Specifically, when the corrosion loss index was 80 or less, it was rated as ◎ (qualified (excellent)); when it was more than 80 and 100 or less, it was rated as 〇 (qualified (good)); when it was more than 100, it was rated as × (unqualified). <Fluidity> In the evaluation of fluidity, the tap flow value of the above kneaded mixture was measured in accordance with JIS R2521. When the tap flow value was 150 mm or more, it was rated as ◎ (qualified (excellent)); when it was 130 mm or more and less than 150 mm, it was rated as 〇 (qualified (good)); when it was less than 130 mm, it was rated as × (unqualified).

[0028] Examples 1 to 8 are cases where the Si / TiO2 ratio is different within the scope of the present invention in a system that does not contain carbon black, and the results show excellent thermal shock resistance and corrosion resistance. On the contrary, Comparative Example 1 is a case where fine silicon powder is not contained, and the result is inferior in thermal shock resistance. Also, Comparative Examples 2 to 4 contain fine silicon powder, but the Si / TiO2 ratio is below the lower limit value of the present invention, and the result is inferior in thermal shock resistance. On the other hand, Comparative Example 5 is a case where the content rate of fine silicon powder exceeds the upper limit value of the present invention, and the result is inferior in corrosion resistance.

[0029] Examples 9 and 10 are cases where the content rate of the titania fine powder is different, but they are within the scope of the present invention and have achieved good results. Examples 11 and 12 are cases where the content rate of the silicon carbide fine powder is different, but they are within the scope of the present invention and have achieved good results.

[0030] From Example 13 to Example 16, in the system containing carbon black, although the Si / TiO2 ratio is different within the scope of the present invention, the results are excellent in thermal shock resistance and corrosion resistance. On the other hand, from Comparative Example 6 to Comparative Example 9, in the system containing carbon black, the Si / TiO2 ratio is outside the scope of the present invention, and the results are inferior in thermal shock resistance.

[0031] Example 17 is a case where non-easily dispersible surface-treated titania fine powder is used. Compared with the case where easily dispersible surface-treated titania fine powder is used, the fluidity is inferior, but the thermal shock resistance and corrosion resistance are sufficient.

Claims

1. In 100% by mass of the refractory composition, it contains 5% by mass or more and 35% by mass or less of silicon carbide fine powder with a particle size of less than 0.3 mm, 3% by mass or more and 20% by mass or less of titania fine powder with a particle size of less than 0.3 mm, and 6% by mass or less of metallic silicon fine powder with a particle size of less than 75 μm, and the carbon black content is 5% by mass or less (including 0), and further, the content rate (Si) of the metallic silicon fine powder, the content rate (TiO ２ ), and the content rate (C) of the carbon black satisfy the following formula (1). A refractory for milling. Si / TiO ２ ≥ 0.11 × C + 0.1 … Equation (1)

2. The refractory for steelmaking according to claim 1, wherein the titania fine powder is surface-treated for easy dispersion.

3. The refractory for steelmaking according to claim 1 or 2, which is used at a location where molten steel slag and molten steel coexist, or at the boundary between molten steel slag and molten steel.

4. The refractory for steelmaking according to claim 1 or 2, which is a casting material used for a blast furnace runner.

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